An unmanned aircraft made from "printed" parts rather than traditional machine-tooled components has been unveiled at the Farnborough Air Show, UK.

Developed at Lockheed Martin's top-secret "Skunk Works" research facility in Palmdale, California, US, the Polecat unmanned aerial vehicle (UAV) is a 28-metre flying wing, weighing four tonnes. It was designed in part to test cheaper manufacturing technologies.

The Skunk Works is no stranger to advanced technology: its successful designs include the ultra-high-altitude U2 spyplane, the SR71 Blackbird - a spyplane which can travel at more than three times the speed of sound - and the radar-invisible F117 stealth fighter.

But speed and stealth performance are not everything: cost matters too. And since UAVs tend to crash more often than piloted planes, the race is on among UAV makers to make them cheaper. The Skunk Works thinks a technique called 3D rapid prototyping, or "3D printing", is the best way to lower costs.

In rapid prototyping, a three-dimensional design for a part - a wing strut, say - is fed from a computer-aided design (CAD) system to a microwave-oven-sized chamber dubbed a 3D printer. Inside the chamber, a computer steers two finely focussed, powerful laser beams at a polymer or metal powder, sintering it and fusing it layer by layer to form complex, solid 3D shapes.

The technique is widely used in industry to make prototype parts - to see if, for instance, they are the right shape and thickness for the job in hand. Now the strength of parts printed this way has improved so much that they can be used as working components.

About 90 per cent of Polecat is made of composite materials with much of that material made by rapid prototyping.

"The entire Polecat airframe was constructed using low-cost rapid prototyping materials and methods," says Frank Mauro, director of UAV systems at the Skunk Works.

"The big advantage over conventional, large-scale aircraft production programmes is the cost saving in tooling as well as the order-of-magnitude reductions in fabrication and assembly time."

By mixing composite polymers with radar-absorbing metals, it is thought that the aircraft can be built with a certain amount of stealth characteristics already built in.

The flexibility lent by 3D printing allowed Mauro's team to design and build the Polecat in only 18 months. "Today's sophisticated UAVs are approaching the cost of equivalent manned aircraft. Polecat's approach is a way to break this trend and demonstrate affordable UAV systems that can be rapidly developed," says Mauro.

The Polecat is also a test bed for autonomous guidance technology, which allows it to do everything from take-off to reconnaissance and landing without the remote guidance of a ground pilot.

This, Mauro hopes, should reduce the current high levels of UAV losses caused by heavy ground pilot workloads.

"This use of rapid prototyping is certainly a revolutionary approach to making an aircraft," says Bill Sweetman, aerospace and technology editor of Jane's International Defence Review. "The classic way is to set up a production line with very heavy-duty fixed metal tools that hold everything in the right place." That is too expensive an approach for the low production runs that reconnaissance UAVs are likely to need, he says.

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